UPDATE 1-UK should extend Brexit withdrawal period if needed -Scottish minister

EDINBURGH, Sept 13 (Reuters) - Britain should extend the time period to negotiate its exit from the European Union to avoid the crippling cost of a "no-deal" Brexit, Scotland's constitutional relations minister Michael Russell said on Thursday.

The publication of advice on what to do if Britain does not clinch an exit deal - so-called technical notices - laid bare the confusion likely to arise, Russell said. He forms part of Nicola Sturgeon's devolved Scottish government, at loggerheads with London over a Brexit it fiercely opposes.

"A no-deal Brexit should be unthinkable, which is why it should be ruled out, if necessary by extending the Article 50 (withdrawal) process," Russell said in a statement.

"These 'Technical Notices' make plain the crippling costs and needless red tape that a no-deal scenario will bring," he added.

EU withdrawal is mired in uncertainty because Britain is the first country to leave the bloc and the process is untested.

Britain formally notified the European Union of its intention to leave the EU by triggering Article 50 of the Lisbon Treaty on March 29, 2017, starting a two-year exit process in which it has yet to reach a divorce agreement.

But an extension would be domestically very complicated for British Prime Minister Theresa May, who is under heavy pressure from sections of her Conservative Party to honour the leaving date.

The other 27 EU member states would also have to agree unanimously to any extension of the negotiations.